Electron-emission material and the activation thereof



Patented May 22, 1928.

UNITED STATES PATENT OFFICE.

THOMAS PHIL]? THOMAS, OF BLOOHFIELD, NEW JERSEY, ASSIGNOB TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

ELECTRON-EMISSION MATERIAL AND THE ACTIVATION THEREOF.

Io Drawing.

This invention relates to material for electron-emission purposes and more particularly to the application of a thorium compound to filamentary material and the decomposition thereof by heat to develop thorium thereon.

An object of my invention is the formation of a coating of metallic thorium on material for electron-emission purposes, by the direct application thereto of a thorium compound and the decomposition thereof by heat to yield free thorium.

Another object of my invention is the activation of material serving as the hot cathode of an electron device by the direct application thereto of thorium oxalate or the like and heating, \vhereb free thorium is developed thereon, or tie application of such to an adjacent electrode or plate, whereby the cathode is activated by heating the plate to decompose the oxalate or the like and transfer liberated thorium to the cathode.

A further object of my invention is the preparation of activated electron-emission material by the application thereto of thorium oxalate held thereon by a suitable binder, such as an amyl-acetate solution of nitrocellulose, and heating the same to cause a decomposition thereof in place, to leave free thorium on the surface of the material.

A still further object of my invention is the manufacture of electron devices comprising an electronemitting filament consisting of a refractory metal filament coated with thorium oxalate, held thereon by a suitable binder, and adapted to be decomposed to yield free thorium for activation and gaseous carbon compounds which are eliminated by a suitable metallic clean-up agent.

Other objects and advantages of my invention will become apparent from the fol lowing description.

Metallic thorium, as is well known, has a high electron emissivity and, for this reason, various methods have been devised for coating material, designed for electron-emission purposes, with metallic thorium, to activate or increase the electron-emissivity thereof. For example, in the copending application of Ralph E. Myers, Serial No. 578,470, filed July 29, 1922, activation of thoriated filaments and assigned to the Application fled April 14, 1983. Serial No. 682,188.

good results in practice, but it entails a preliminary heating operation of the filamentary material, prior to its introduction into an electron device. That is, the filamentary material is heated in a hydro-carbon atmosphere to precondition it for the development of thorium thereon when used as the hot cathode in an electron device.

According to my invention, I obviate the necessitv of the preliminary heat treatment by applying, to the filamentary material, a compound of thorium, decomposible by heat to yield free thorium on the surface of the filamentary material. The preferred material used for this purpose is thorium oxalate, although I do not wish to be restricted tothe precise compound mentioned, as any solid thorium compound, which decomposes on heating to liberate free thorium therefron'i before it evaporate, may be employed for this purpose. The thorium oxalate. in powdered form, is preferably mixed with a suitable binder solution, for example, nitro-cellulose dissolved in amyLacetate, and applied to the filamentary material as a paint or varnish, but any other method suitable for afiixing the thorium compound firmly to the filamentary material may be employed.

The material so treated may then be attached to a suitable mount including a plate, to which is preferably attached metallic clean-up material, such as aluminum, magnesium or both and introduced into an evacuated envelope as the hot cathode or electronemitting filament of an electron device. The plate may then be heated in any desired manner, after the device is evacuated, for

the oxalate, liberate free thorium and cansing the filamentary material to be c0ated l0 therewith.

In testimony whereof, I have hereunto subscribed my name this 13th day of April, 1923.

THOMAS PHILIP moms, 

